Constructive versus Destructive Heterogeneity in Porous Electrodes of Lithium-Ion Batteries

Abstract

We introduce an efficient framework for investigating the heterogeneity in the battery porous electrodes and its impacts on the performance and longevity of the lithium-ion batteries. A phenomenological picture based on theory and experiment is presented to show how the spatial variations in the local porosity and thickness in a porous electrode result from a microscopically inhomogeneous slurry. A series of analogous bilayer LiNi0.6Mn0.2Co0.2O2 porous electrodes with different levels of heterogeneity, induced by a non-uniform distribution of carbon, is prepared as a model experimental system and established as a powerful tool in formalizing the concept of heterogeneity. We identify and distinguish between the constructive and destructive heterogeneity as the two shades of non-uniformity in the porous electrodes. Depending on the degree of heterogeneity, we observe up to 20% decline in the rate performance of the electrodes. The destructive and constructive heterogeneity in the analogous electrodes are manifested in 5 fold increase and 2 fold decrease, respectively, in the aging rate of Li4Ti5O12|LiNi0.6Mn0.2Co0.2O2 cells relative to that of a cell with a homogenous electrode after 200 cycles at 1C.